Electron affinity decreases down the group but increases across the period while ionization energy decreases down the group and increases across the period.
The term electron affinity refers to the energy released when an electron accepts electrons to form negative ions while ionization energy is the energy required to remove an electron from an atom.
The both concepts are opposing and sometimes confusing. However, electron affinity decreases down the group but increases across the period while ionization energy decreases down the group and increases across the period.
This occurs because, among the main group elements, more shells are added as you move down the group. This means that the outermost electrons are more shielded from the nucleus thereby making it easier to remove them owing to decrease in Coulumbic attraction between the outermost electrons and the nucleus.
However, across the period, one electron is added at a time. The size of the nuclear charge is increased without increasing the shielding. As such, the magnitude of Coulumbic attraction between the outermost electrons and the nucleus increases thereby making the outermost electron more tightly bound and difficult to remove. The ionization energy, therefore, increases.
As the atom becomes smaller, it becomes easier for the atom to accommodate more electrons.Hence, as the atomic size decreases across the period, electron affinity increases accordingly.
Learn more: https://brainly.com/question/2060520
